The invention relates to an apparatus and method for application of various chemicals and compounds to fabric and fiber webs of woven and nonwoven construction, knitted webs, and laminated webs or batts of various constructions. Certain of these webs have constructions in which variations in thickness and density exist as well as surface irregularities. It thus becomes difficult to coat the web while traveling on a coating machine so that the web has a smooth coating layer of uniform thickness.
Heretofore, coating apparatus and methods have been provided which use a blade to spread a coating material over and into the web. Some coating penetrates the web and some remains on the surface to form a molecular bond. However, application of the coating layer varies due to depressions (thin spots) and islands (thick areas) as well as other surface regularities. Various biasing arrangements have been provided for the coating tables of prior apparatus and methods to bias a blade and web together. For example, a foam table has been used to yieldably urge a web and blade which spreads a coating material on the web.
In U.S. Pat. No. 2,614,522 a spring arrangement is shown for yieldably urging a bottom roll against a sheet on which a coating is applied to an upper surface. However, the biasing provided by the spring is non-uniform and larger variations in thickness produce larger biasing forces all of which result in non-uniform coating layers.
Furthermore, if an application roll is used to contact the web and apply coating material, non-uniform forces produced by foam tables and spring arrangements cause deviations in the contact angle between the web and application roll. The angle of contact between the web and application roll directly influences the coating construction. In the case of spreading with a scrape blade, the amount of pressure between the blade and web also determines the coating construction. Any variations in web
Heretofore, coating apparatus and methods have been provided which use a blade to spread a coating material over and into the web. Some coating penetrates the web and some remains on the surface to form a molecular bond. However, application of the coating layer varies due to depressions (thin spots) and islands (thick areas) as well as other surface regularities. Various biasing arrangements have been provided for the coating tables of prior apparatus and methods to bias a blade and web together. For example, a foam table has been used to yieldably urge a web and blade which spreads a coating material on the web.
In U.S. Pat. No. 2,614,522 a spring arrangement is shown for yieldably urging a bottom roll against a sheet on which a coating is applied to an upper surface. However, the biasing provided by the spring is non-uniform and larger variations in thickness produce larger biasing forces all of which result in non-uniform coating layers.
Furthermore, if an application roll is used to contact the web and apply coating material, non-uniform forces produced by foam tables and spring arrangements cause deviations in the contact angle between the web and application roll. The angle of contact between the web and application roll directly influences the coating construction. In the case of spreading with a scrape blade, the amount of pressure between the blade and web also determines the coating construction. Any variations in web thickness and density and any surface irregularities cause variations in angles of contact and blade pressures. The non-uniform biasing arrangements used heretofore have not been able to provide smooth uniform coating for webs having thickness and density variations and surface irregularities.
According an important object of the present invention is to provide an apparatus and process for applying a smooth uniform coating to a web having density and thickness variations and surface irregularities.
Another important object of the present invention is to provide a method and apparatus for coating a web having variations and irregularities in its surface wherein the web is supported during coating so that a uniform pressure is exerted between the web and a scrape blade during coating.
Still another important object of the present invention is to contact a traveling web having thickness variations and irregularities in its surface against a coating transfer roll with even pressure so that a constant angle of contact between the web and roll results.